Lamp starting and operating circuit



Feb. 16, 1965 1.c. RETzl-:R 3,170,084

LAMP STARTING Aun OPERATING cIRcuIT Filed Nev. s., 1961 FIG.

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United States PatentOiiice inghouse Electric Corporation, East Pittsburgh, Pa., a'

corporation of Pennsylvania Filed Nov. 3, 1961, Ser. No. 150,065 Claims. (Cl. 315-173) This invention relates to an energizing circuit for gaseous discharge devices and, more particularly, to an improved circuit for starting and operating a highpressure gaseous discharge lamp wherein the lamp is operated on direct current from an alternating voltage source.

While gaseous discharge lamps such as the so-called short-arc mercury vapor lamps are customarily started and operated from an alternating voltage source, there are times when the improved arc stability obtained with direct-current operation is highly desirable, as when the lamp is used in a sensitive instrument such as an optical comparator for example. Since alternatingV current is more readily available, an operating circuit having rectifying means which will convert A.C. voltage to the required D.C. voltage is generally used in such applications. The most practical arrangement is to employ a fullbridge rectifier. Starting and operating circuits utilizing such bridge rectifiers are disclosed in U.S. Patent Nos. 2,757,318 to Noel et al.; 2,871,412 to Lord; 2,892,126 to Popa; and 2,975,333 to Bird.

While the prior art starting and operating circuits of the type described in the above-mentioned patents provide the elevated voltages required to start the lamp and the direct current to operate it, they are relatively complicated and expensive and produce starting voltages that are much too high for low-watage short-arc lamps and necessitate the use of rectifying elements having a high inverse voltage rating. Such low-wattage short-arc lamps are generally of the so-called single-ended construction wherein the lead wires are sealed through the same end of the outer envelope. Because of the relatively close spacing between the lead wires and lamp contacts, it is very important that the starting voltage applied to the lamp be controlled and kept within a prescribed limit in order to avoid any possibility whatsoever of destructive arcs occurring between the lead-in conductors or within the sockets in which such single-ended lamps are used.

lt is, accordingly, the general object of the present invention to provide an improved circuit for starting and operating a gaseous discharge device that requires a higher starting than operating voltage and a D.C. operating voltage.

Another and more specific object is the provision of a simple, inexpensive starting and operating circuit for lowwattage short-arc gaseous discharge lamps that will provide a smooth DC. operating voltage and a controlled starting voltage capable of igniting the lamp without damaging it or the components in the D.C. operating circuit.

The aforesaid objects, and others which will become apparent to those skilled in the art as the description proceeds, are achieved in accordance with this invention by providing a full-wave bridge rectifier circuit and a switchoperated A.C. starting circuit that is energized and coupled to the rectifier circuit only during the starting cycle. The A.C. output of the starting circuit is such that when it is superimposed on the DC. output of the rectifying circuit a controlled elevated voltage is produced that quickly starts the lamp without damaging it or the rectifying elements.

A better understanding of the invention Iwill be obtained by referring to the accompanying drawing wherein:

FIG. l is a schematic diagram of a starting and operat- 3,1?0,084 Patented Feb. 16, 1965 ing circuit according to the invention, the auxiliary A.C. starting portion thereof being energized and shown in heavy outline to indicate the components that are in the circuit only during the starting cycle:

FIG. 2 is the same circuit as that illustrated in FIG. l but shows the conversion thereof to a D.C. operating circuit effected after the lamp has been started, which operating circuit is shown in heavy outline; and

FIG. 3 is a side elevational view of a 250 watt short-arc mercury lamp illustrative of the low-wattage type discharge lamp that requires the controlled starting voltage produced by circuits embodying the present invention.

Although the improved circuit of this invention can be employed to start and operate various types of gaseous discharge devices which require a D.C. operating voltage and a higher starting than operating voltage, it is particularly adapted for use with low-wattage short-arc lamps of single-ended construction and has accordingly been so illustrated and will be so described.

The circuit With specific reference to the drawing, in FIG. l there is shown a combined starting and operating circuit for a gaseous discharge lamp 8, such as a high-pressure mercury-vapor discharge lamp, which circuit comprises a voltage converting means such as a full-wave rectifier 10 consisting of four rectifying elements 11, 12, 13 and 14 connected in the usual bridge relationship. The input terminals of the bridge rectifier 10 are connected to a suitable source of alternating voltage (not shown) by means of input conductors 15 and 16 and input terminals 18 which together comprise an input circuit. The output terminals of the rectifier are connected to the lamp terminals by a pair of conductors 19 and 2b, which conductors constitute the output circuit of the rectifier. A suitable current-limiting or impedance means such as a resistor 22 is connected in the output circuit in series with the lamp 8 to provide a ballast that regulates the lamp operating current in the well-known manner. A capacitor 24 is connected across the output circuit of the rectifier in parallel with the lamp 8, and an inductive reactor 26 is also connected in the output circuit in series with the lamp. The foregoing capacitor and inductor network provides a filter located between the lamp 8 and rectifier 10 that smooths out the pulsating D.C. voltage output of the rectifier and limits the ripple current to a low value.

Experience has shown that when the inductive reactor 26 is located iu the output circuit at a point closer to the rectifier 10 than the filter capacitor 24, the resultant inductive-input filter prevents excessive current from flowing through the filter capacitor and drastically shortening its life. This type filter network is, accordingly, preferred and is shown in FiGS. l and 2.

The aforementioned rectilier 10, conductors 15, 16, 19, 29, terminals 13, ballast 22, and filter network constitute the normal D.C.operating portion of the circuit.

lt has also been found desirable to connect a by-pass capacitor 28 across the output circuit of the rectifier lil in parallel with the lamp 8 to protect the rectifier elements from transient voltages and from the A.C. starting voltage. This by-pass capacitor is much smaller than the iilter capacitor 24 and it is preferably located at a point across the rectifier output circuit that is closer to the rectifier 10 than the inductive reactor 26 and iilter capacitor 24, as illustrated in the drawing.

Since the lamp 8 is a gaseous discharge device it requires a higher starting than operating voltage. This elevated starting voltage is obtained according to the invention by providing an auxiliary A.C. starting circuit which consists of a transformer 30 having a primary winding 31 and secondary winding 32, and a capacitor 34 and suitable current-limiting means, such as a resistor 36,

J that are connected in series with the secondary winding. The primary winding 31 is controllably connected by means of a single-action multiple-contact switch 33 and conductors 39 and 4f) to the input circuit of the rectifier 10. The serially connected secondary winding 32, capacitor 34 and resistor 36 are connected by means of another pair of conductors 41 and 42 to a second pair of switch contacts (that are normally open as shown in FIG. 2) and across the rectifier output circuit on the load side of the inductor-capacitor lter network. The switch 38 is spring biased and normally open so that the starting circuit is energized and coupled to the D.C. operating circuit only when the starting switch is actuated.

To avoid a large drop in the A.C. starting voltage the transformer secondary 32 and serially connected resistor 36 and capacitor 34 are preferably connected across the output circuit of the rectifier at a point closer to the lamp 3 than the resistor ballast 22.

In order to make the filter network in the DC.- operating portion of the circuit a high impedance during the starting cycle and thereby prevent the A.C. starting current from flowing in this direction rather than through the lamp 8, a blocking resistor 44 is preferably connected in series with the capacitor 24. The full filtering effect of the capacitor 24 is subsequently regained during normal operation of the lamp by connecting the blocking resistor to a third set of contacts in the switch 38 through shunting conductors 45 and 46, which contacts are normally closed as shown in FIGURE 2. Thus, the blocking resistor 44 is only in the circuit when the starting switch 38 is depressed and is shunted when this switch is released and the lamp is operating normally.

To obtain maximum filtering effect the aforesaid filter network is connected in the output circuit of the rectifier at a point closer to the rectifier than either the transformer secondary 32 or the resistor ballast 22, as shown in the drawing.

Operation From the foregoing it will be seen that when the starting switch 38 is actuated the transformer primary winding 3l is connected to the input circuit of the rectifier 10 and to the A.C. power supply, and the transformer secondary winding 32 is coupled through the capacitor 34 and resistor 36 to the output circuit of the rectifier i0 in parallel with the lamp 8. The starting switch 33 thus controls the energization of the starting circuit and connects it to the operating circuit only during the starting cycle, as is indicated by the heavy line showing of the starting circuit in FIGURE 1.

The A.C. output of the starting circuit is thus superimposed on the filtered DC. voltage output of the fullwave rectifier 10 thereby producing a controlled elevated voltage that is applied to the lamp. The capacitor 34 immediately charges to the voltage appearing across the lamp 8, and when the starting gas within the lamp is ionized and renders the lamp conductive, the capacitor discharges through the lamp. If current does not continue to flow through the lamp, the capacitor 34 will repeatedly recharge and then discharge through the lamp, as long as the switch 3S is closed, until current flows continuously at which time the arc voltage of the lamp will be low enough to permit the lamp to be operated directly on the D C. voltage output of the rectifier.

The resistor 36 limits the starting current from the A.C. starting circuit to a safe value whereas resistor 22 limits the D.C. current from the rectifier 10.

After the lamp 8 has started, the starting switch 38 is released thereby disconnnecting the transformer primary 31 from the input circuit of the rectifier 10, and the transformer secondary 32 from the output circuit of the rectifier. The starting circuit is accordingly deenergized and disconnected from the D.C.operating circuit and the lamp 8 is operated directly from the DC. circuit, as indicated by the heavy,I line showing thereof in FIGURE 2.

It will be noted that when the starting switch 3S is in its normally-open position (see FIG. 2) the third set of contacts connected to the conductors and 46 shunting the blocking resistor 44 are closed thereby removing this resistor from the filter portion of the D.C.operating circuit.

Since the transformer 30 is only in the circuit during the starting cycle it only has to carry the starting current which is much lower than the operating current. This is a distinct advantage since the current-carrying capacity and wattage rating, and thus the cost, of the transformer can be reduced proportionally compared to that required if either of the transformer windings were in the operating portion of the circuit.

In order to prevent short-circuiting the lamp 8 when the starting circuit is energized the transformer 3i) is of the so-called isolation type wherein the primary and secondary windings are electrically isolated from each other, in contrast to an auto-transformer for example.

A ppl icatz'on Circuits embodying the principles of this invention are especially adapted for use in conjunction with a singleended low-wattage short-arc lamp S of the type shown in FIG. 3 which lamp comprises, in general, an inner arc tube of quartz or the like that contains two electrodes 52, a filling of a suitable ionizable gas such as argon or the like, and a charge of mercury. The arc tube is sealed Within an outer tubular envelope 54 and is supported therein by a pair of rigid lead-in conductors 55 and 56 which pass through a re-entrant stem 58 that is sealed to the end of the outer envelope. A prefocus type base 60 is secured to the sealed end of the outer envelope thereby providing a lamp that is similar in appearance and size to a conventional incandescent projection lamp.

The space between the inner arc tube 50 and the outer protective envelope 54 may be evacuated or filled with a suitable inert gas such as dry nitrogen. In either case, it has been found desirable to limit the starting Voltage applied to lamps of this construction and size to about 400 volts maximum in order to eliminate the possibility of destructive arcs occurring between the relatively closely spaced lead-in conductors, or within the base 60 or lamp socket.

Specific Example As a specific example of the relative size of the various circuit components required for a particular lamp design, it has been found that a Z50-Watt single-ended short-arc lamp of the type illustrated in FIG. 3 can be started within about two seconds after the switch 33 is actuated by employing an auxiliary A.C. starting circuit consisting of a 60 Ato 100 watt transformer 30 having a conversion factor of 1 to l, and a 2 microfarad 330 volt capacitor and a ohm (2 watt) resistor connected in series with the transformer secondary. When the transformer primary was connected to a A.C. voltage supply, the aforesaid starting circuit had an output of 162 volts which was superimposed on the D.C. voltage output of the rectifier 10. When a full-wave silicon diode type rectifier having an output circuit with a 11.5 ohm ballast resistor, a 300 microfarad 450-volt filter capacitor, a 100 millihenry inductive reactor, a 0.5 microfarad 60G-volt by-pass capacitor, and a 15,000 ohm blocking resistor (arranged as shown in the drawing) was connected to the same A.C. supply it had an output of about 158 volts D.C. Thus, `a total of approximately 320 volts was applied by this particular circuit to the lamp, which voltage was sufficient to start the lamp within approximately 2 seconds Without exceeding the 400 volt limit established to eliminate any possibility of arcing between the lamp lead-in conductors, or exceeding the peak inverse voltage rating of the rectifying elements which, in the case of the silicon diode rectifiers used in this particular circuit, was 500 peak inverse volts. The D.C. output of the rectifier had about a 3% ripple factor so that the lamp arc was very stable.

It will be seen from the foregoing that a starting and operating circuit has been provided which is not only simple and inexpensive to make but which generates a controlled starting voltage that reliably starts a gaseous discharge lamp in a very short time without subjecting it or the rectifying elements in the DC. circuit to excess voltages. y

While a specific embodiment has been described in detail by way of illustration and example in accordance with the patent statutes, it will be understood that various modifications in both the arrangement and size of the circuit components can be made without departing from the spirit and scope of the invention.

I claim:

1. The combination comprising: a bridge rectifying circuit adapted to operate a gaseous discharge lamp on direct current from an alternating voltage source; an alternating current starting circuit comprising a capacitor, a resistor, and a transformer having a primary and a secondary Winding; and circuit means including a switch having one set of contacts in a circuit connecting the primary winding of said transformer to the input of said rectifying circuit, and a second set of contacts'in av circuit connecting the secondary winding of said trans# former, capacitor and resistor in series` across the output of said rectifying circuit.

2. The combination of a rectifying circuit and an alternating current starting circuit as set forth in claim l wherein, said rectifying circuit includes impedance means for limiting the lamp operating current, and said serially connected secondary winding, capacitor and resistor are connected across the output side of said rectifying circuit at a point closer to the lamp than said impedance means.

3. The combination of a rectifying circuit and an alternating current starting circuit as set forth in claim 1 wherein the primary and secondary windings of said transformer are electrically isolated from each other.

4. A circuit for starting and operating a gaseous discharge lamp that contains an ionizable medium and ,requires a higher starting than operating voltage, said circuit comprising a full-wave bridge rectifier having an input circuit and anoutput circuit, first current-limiting means in said output circuit for regulating the lamp operating current, a filter comprising a first capacitor and an inductive reactor in said output circuit connected between said rectifier and 'said lamp, a transformer having a primary and a secondary winding, means including a switch for temporarily connecting said primary winding to the input circuit of said rectifier and said secondary Lwinding across the'output circuit of said rectifier in parallel with said lamp, a second capacitor and a second current-limiting means connected in series with each other and with said secondary winding, said transformer together with said second capacitor and said second current-limiting meansconstituting an auxiliary alternating current starting circuit that is controlled by said switch and, when energized, is adapted to produce a predetermined alternating current voltage that is superimposed on the direct current voltage output of said rectifier and thereby apply a voltage to said lamp of sufficient magnitude to start it without exceeding the peak inverse voltage rating of said rectifier.

5. A starting and operating circuit as set forth in claim 4 wherein a by-pass capacitor is connected across the output circuit kof said rectifier at a point closer to said rectifier than said filter.

6. A starting arid operating circuit as set forth in claim 4 wherein said first current-limiting means comprises a resistor connected in series with said lamp.

7. A starting and operating circuit as set forth in claim 4 wherein, said filter capacitor is connected .across the output circuit of said rectifier at a point closer to said rectifier than the secondary winding of said transformer, and said inductive reactor is connected in series with said lamp at a point in said output circuit closer to said rectifier than said first capacitor thereby providing an inductive-input type filter.

8. A starting and operating circuit as set forth in claim 7 wherein a third current-limiting means is connected in series with said first capacitor and to said switch by `conductor means in a manner such that said third currentlamp, a first capacitor in said output circuit connected in parallel with said lamp, an inductive reactor in said output circuit connected in series with said lamp, said first capacitor and inductive reactor being electrically oriented with respect to each other and to said rectifier to provide an inductive-input lter in the output circuit of said rectifier, a second capacitor in said output circuit connected in parallel with said lamp at a point closer to said rectifier than said filter, a transformer having a i primary and a secondary winding, a starting switch, first conductor means adapted to connect said primary winding to said input circuit when said starting switch is actuated, a third capacitor anda resistor connected in series with said secondary winding, second conductor means adapted to connect said serially connected secondary winding, third capacitor and resistor across the output circuit of said rectifier in parallel with said lamp when said starting switch is actuated, said'transformer together with 'said first and second conductor means and third capacitor and resistor comprising a starting circuit that is energized and coupled to the output circuit of said rectifier only when said starting switch is actuated and thereby establishes an elevated voltage sufficient to start said lamp without exceeding the peak inverse voltage rating of the elements comprising the bridge rectifier.

10. A starting and operating circuit as set forth in claim 9 wherein, the primary and secondary windings of said transformer are electricallyisolated from each other, and the output circuit of said, rectifier includes'a second resistor that is connected to said starting switch by a third conductor means and is placed in series with said first capacitor only when said starting switch is actuated and Von Henke July l14, 1942 `Popa June 23, 1959 3,066,243 Mutsiiier Nov. 27, 19,62 

1. THE COMBINATION COMPRISING: A BRIDGE RECTIFYING CIRCUIT ADAPTED TO OPERATE A GASEOUS DISCHARGE LAMP ON DIRECT CURRENT FROM AN ALTERNATING VOLTAGE SOURCE; AN ALTERNATING CURRENT STARTING CIRCUIT COMPRISING A CAPACITOR, A RESISTOR, AND A TRANSFORMER HAVING A PRIMARY AND A SECONDARY WINDING; AND CIRCUIT MEANS INCLUDING A SWITCH HAVING ONE SET OF CONTACTS IN A CIRCUIT CONNECTING THE PRIMARY WINDING OF SAID TRANSFORMER TO THE INPUT OF SAID RECTIFYING CIRCUIT, AND A SECOND SET OF CONTACTS IN A CIR- 